I went with the chrome-plated steel. They would only do the cast aluminum with 2" letters due to the number of characters that I needed(16). I got the chrome-plated steel with 3" letters and I really liked the idea of the bright chrome-plated, forward slanted letters better in my ambulance anyway. Were I buying name plates for my hearse, I would have probably gone with the cast aluminum. My plates read "RADIO-DISPATCHED" with a slight forward slant, so I was not going for a formal look anyway.
The cast aluminum plates are still about $250.